Flexible Tank for a Shipping Container

ABSTRACT

A flexible tank is used to transport liquids or semi-liquid material in a shipping container on a railroad car. It has an inner tank and at least one end closure with alternating interlaced hollow loops from two separate exterior layers. A nylon rope or similar securing element is passed through the hollow loops to use the exterior layers in an end closure to constrain the inner tank. An end flap may be welded to an exterior layer and positioned between the inner tank and the end closure. The hollow loops may be formed by folding over the exterior layers and cutting out complementary portions so the loops are in an alternating interlaced pattern. Capacity bands located around the periphery of the flexible tank suppress expansion of the flexible tank at their respective locations.

BACKGROUND

Lengthy shipments of goods frequently involve multiple modes oftransport, such as ocean going vessels, railroad cars and trucks.Standardized intermodal shipping containers facilitate intermodaltransport as they allow a variety of goods to be easily moved from placeto place in ports and warehouses, and between ships and railroad cars.Some organizations, such as the International Standards Organization(ISO), have developed and continue to maintain standards for shippingcontainers such as size, location of doors, and the use of specificcorners or fittings so that a container can be securely gripped andmoved by lifting equipment. The ability to use a standardized shippingcontainer is an advantage because the container handling equipment andlogistics of making shipments of special kinds of goods is simplifiedwhen a particular customized shipping container is not necessary. Forexample, a large quantity of liquid can be transported by placing theliquid inside of a flexible tank in a shipping container also usable fordry goods and then that container can preferably be treated like anyother shipping container without regard to the nature of its contents.

There is specialized equipment used for transport by road, rail and shipof bulk liquid products. However, it is desirable to take advantage ofstandard container equipment to realize cost savings. Standardizedshipping containers are prevalent in both domestic and internationaltrade lanes, and thus cheaper to use. For example, 40′ or 53′ shippingcontainers are readily and commonly available in North America. Theprevalence or ubiquity of such larger shipping containers in somemultimodal transport routes is such that it can be economicallybeneficial to use a flexitank in them with the same capacity as used insmaller 20′ shipping containers.

These larger containers have a much higher internal volume than smaller20′ shipping containers. Due to weight restrictions, it can be difficultto take full advantage of the larger internal volume. The liquids to beshipped can have vastly different specific gravity (weight per gallon),and the volume of the liquid that can be shipped within the weightrestriction varies accordingly. Conventional flexitanks are typicallymass produced and are of a single capacity. This is a disadvantage for alarger shipping container with high internal volume where it is somewhatmore possible to ship different volumes of liquids while remainingwithin the weight restriction. There are also other disadvantages tolarger shipping containers that must be solved when shipping liquids.

For example, a 40 foot container may not always facilitate the use of abulkhead. Flexible tanks designed for a 20 foot container with abulkhead are typically longer than the internal length of the containerso that the ends of the flexitank are supported by the front inside wallof the container and a bulkhead panel placed across the door opening atthe rear wall. Therefore, the flexitank for a 20 foot shipping containermay be, for example, 23 feet long. A 40 foot shipping container may notfacilitate use of a bulkhead and the front wall, so the flexible tankmust be freestanding, without relying on the availability of any endwall or bulkhead support.

The flexible tank should not deform any of the side or end walls of thecontainer in which it is placed. Intermodal shipping containers aresometimes stacked or placed very close together in cargo holds ofvessels or ports, with only a few inches of tolerance, and an outwardlydeformed wall may interfere with or prevent placement of the container.The side walls of a 40-foot container are generally more susceptible todeformation than the side walls of a 20-foot container if for no otherreason that they are longer and have no additional support. There is alimit to the amount of force that should be placed on the side wall of a40-foot container by a flexible tank full of liquid.

But the largest disadvantage associated with the use of flexible tanksinside of larger shipping containers is the increased possibility ofleak or rupture if the flexible tank for a 20-foot container is simply“lengthened” or made larger for a 40-foot container. Sudden movement cancause a rupture of a flexitank (even if there is no manufacturing defector “weakness” in the flexitank). Sudden starts, stops or impacts canresult in large waves that produce enormous pressure on the ends of theflexible tanks. The danger of a flexible tank rupture or leak dependsgreatly on the volume of the liquid inside of it and the length of theflexible tank from end to end. The liquid dynamics are dramaticallydifferent depending on the shape, proportion and volume of a flexitank.In particular, the flexitank for a 40′ container will typically have alower profile (height) than the flexitank for a 20′ foot container.FIGS. 3(a)-3(c) show the sewn end seams in a prior art flexitank. Theseend seams are susceptible to liquid dynamics (shown by the arrow in FIG.3(c)) that impact the end seams at the intersection where they are sewntogether, forcing the two halves to separate apart and away from eachother.

So even when a larger shipping container is available, a larger versionof a known flexible tank has historically not been practical due to therisk of rupture. For example, in U.S. Patent Application Publication No.2017/0144833 filed by Environmental Packaging Technologies, Inc., threedifferent flexible tanks are used in a 40-foot or 53-foot containerrather than one larger flexible tank. Such a system has thedisadvantages that each flexible tank has to be individually loaded andunloaded, and the cost of the three flexible tanks is more than it wouldbe if there were but a single flexible tank. A single larger flexibletank has historically not been possible in larger shipping containersbecause of the likelihood of rupture or leak.

This risk of leakage of flexible tank rupture is even greater for amultimodal shipment where the larger shipping container will be partlytransported by railroad. Railroad cars are large and heavy, especiallywhen loaded. Railroad cars are typically interconnected to each other byrunning them into each other to cause them to be hooked together in aprocess sometimes referred to as shunting. Even at a low speed, thesecollisions create very large and very sudden forces of deceleration,such as 2G's, that are similar to those experienced in a sudden andcomplete full stop. But this problem has been solved by the preferredembodiments of the invention. In particular, the flexible tanks of thepreferred embodiments of the invention, although freestanding,disposable, and made especially for use in 40-foot shipping containers,will not leak or rupture even when repeatedly subjected to the impactsof railroad car collisions.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1(a) shows a flexitank for a 40-foot shipping container, accordingto a preferred embodiment of the invention, when it is partially filledwith liquid.

FIG. 1(b) shows an optional preferred embodiment utilizing capacitybands.

FIG. 2 is an illustration of a railroad car impact which the preferredembodiment of the invention undergoes without leaking, rupturing, ordamaging the container in which it is placed.

FIGS. 3(a)-3(c) show the end seam of a prior art flexitank.

FIG. 4 shows an improved strength end closure of the preferredembodiments.

FIG. 5 shows is an illustration of the assembly of the end closure inFIG. 4.

FIG. 6 is an exploded view of the end closure in FIG. 4.

FIGS. 7(a)-7(e) show the steps of forming a flexitank according to thepreferred embodiment.

FIG. 8 is a perspective view of an end closure in the preferredembodiment of the invention.

FIG. 9 shows an optional preferred embodiment in which an end cap isused to further strengthen the end closures of the flexitank.

FIG. 10 shows an end view of an exemplary bulkhead used in conjunctionwith the flexitank of one of the preferred embodiments.

FIG. 11 shows a side view of an exemplary bulkhead used in conjunctionwith the flexitank of one of the preferred embodiments.

THE PREFERRED EMBODIMENTS OF THE INVENTION

Of course, the actual impacts on a larger shipping container when it ison a railroad car during part of a particular multi-modal shipmentcannot be known in advance with certainty. However, they can bepredicted and simulated. The preferred embodiments of the invention arebelieved to be the first to satisfactorily survive these impacts withoutleak, rupture, buckling of the bulkhead securement bars, damage ordeforming of the container walls. A typical simulated impact test isshown in FIG. 2.

The railroad car with the shipping container and flexible tank isreleased on an approximate 0.8% downgrade of railroad track toward astring of empty anvil cars with standard draft gears and a combinedweight of 250,000 lbs (113.40 metric tons), with the airbrakes set onall impact vehicles, and the handbrakes set on the first and last cars.The predetermined location is selected such that, at the point ofimpact, the railroad car carrying the flexitank has a speed ofapproximately 4-6 miles per hour (mph).

FIG. 1(a) shows a preferred embodiment of a flexitank according to theinvention resting on the floor of the shipping container (horizontal cutaway view). The flexitank is shorter than the internal length of theshipping container and its ends fall short of the end walls of thecontainer. It consists of three layers of low density polyethylene(preferably 125×2 microns thick) plus an outer layer of wovenpolypropylene outer sleeve or cover (preferably 550×2 microns thick).The cover provides additional strength along the length of the flexitankthat will absorb and control the internal liquid dynamics duringtransport. The cover for the flexitank is constructed from one layer ofa 610 gram per square meter vinyl fabric on a base reinforcing scrim ofeither a 14×14 or 20×20 per centimeter polyester thread. Such arelatively high thread count of the scrim provides added strength forthe carriage of liquids with a specific gravity higher than water. Thediameter of the covering external layers is dependent on the desiredcapacity of the flexitank. There may be a single fill/discharge port onthe top of the flexitank or there may a top fill port and a dischargevalve at an end of the flexitank.

The preferred dimensions of a flexitank for a 40-foot containeraccording to the preferred embodiments of the invention is 40.5 feet inlength and 9.6 feet wide, and approximately 27 inches in height whenloaded so as to have a capacity of 5,812 US gallons (22,000 liters).When filled to capacity, the top is somewhat dome-shaped, being higherin the middle than it is at its ends and sides. See FIG. 1(a). Anotherimportant aspect of the preferred embodiments is that the flexitank isnot filled to capacity. This is counter-intuitive given the knownconcern over waves causing ruptures at the ends of flexitanks. The priorthinking was that, if the flexitank was completely filled such that wasno empty air space, waves could not form that would travel from end toend, potentially causing ruptures. But the inventors have surmised thatliquid dynamics are still created by sudden impacts that stress theends. In addition to the improved end closures, the preferredembodiments also take a different approach with respect to capacity. Theflexitank is intentionally not filled to capacity. For example, for aflexitank with a capacity of 5,812 US gallons (22,000 liters), it isonly partially filled, preferably with 5,425 US gallons (20,560 liters).

Capacity bands can optionally be used at various points along the lengthof the flexitank to adjust the capacity of the flexitank to, forexample, permit the shipping of liquids of different specific gravitieswhile remaining within the weight restriction. The lengths of the bandsare somewhat less than the circumference of the flexitank when it iscompletely filled to capacity. The bands thus “squeeze” the flexitankimparting a sort of four hump camel shape to the flexitank and affectingthe capacity of the flexitank as shown in FIG. 1(b). The number andlength of the bands affect the flexitank capacity to different extents.The number of bands can be increased and/or the bands can be madeshorter to reduce the capacity. The preferred connection length of thebands for the dimensions provided above accommodates a circumference of122 inches. Preferably, the bands are disposed in a symmetrical fashionalong the length of the flexitank so as to avoid any disproportionateeffect on the liquid dynamics. There may be three bands with the middleband positioned at the center. Or there could be an even number of bandsspaced proportionally along the length of the flexitank.

An important aspect of the capacity of the bands is that they are aseparate piece from the main part of the flexitank, and selected at thetime of installation according to the liquid to be shipped. This allowsthe main part of the flexitank to be mass produced and the capacitythereof optionally decreased by selective use of bands. The capacitybands are not sewn into or otherwise secured on the main part of theflexitank. They surround the exterior and act somewhat like a belt for aperson's waist, relying on the squeezing to keep them in place. It isimportant that the bands to do not have buckles, or other items withedges, to set their length or keep them in place. Testing has shown thatthere is significant abrasion between the capacity bands and theflexitanks during shipment, and care must be taken that the capacitybands themselves do not cause a leak or puncture. Preferably, the endsof the capacity bands are sewn together to form a continuous loop. Asuitable construction of the capacity bands is a two inch width fabricconstructed from a mixture of polyester and nylon materials.

Another key feature of the preferred embodiments are improved endclosures shown in FIGS. 4-8. They seal both ends of the tank and provideadditional strength to the heat sealed end seams of the inner tank whencompared to the prior art sewn ends shown in FIGS. 3(a) to 3(c),preventing any bursting of the of the seam when under pressure from theliquid forces placed upon it. The result is a flexitank that is overallmuch stronger on the ends than the conventional flexitank.

A process of forming a flexitank according to a preferred embodiment ofthe invention is shown in FIGS. 7(a)-7(e).

In the first step, long and narrow fabric layers are welded togetherlongitudinally, preferably by radio frequency (RF) welding, to form thetop and bottom external layers. The ends of the top and bottom layersare welded back onto itself as shown in FIG. 7(a) to form a loopsufficiently large to accept a nylon rope.

In the second step, the end flap is welded to the inside of the bottomlayer about 30 to 36 inches from each end of the bottom layer. This endflap is preferably the same fabric as the top and bottom outer layers.The end flap has the same width as the top and bottom layers and alength of approximately 7 to 8 feet. At this point, the end flap extendspast the end of the bottom layer as shown by dashed line A in FIG. 7(b).When manufacture of the bag is complete, the end flap will be positionedas shown by dashed line B in FIG. 7(b). It is to be understood that,although not shown in the cross-section view, the longitudinal sides ofthe top and bottom layer are welded to each other so as to form an openended tube.

In the third step, the looped ends of the top and bottom layers are cutat the same points to form corresponding equal sized sections of thelooped ends as shown in FIG. 7(c). Odd loops are removed from one of thelayers and even loops are removed from the other layer so that thelayers have alternating interlaced loops in the manner of a door hinge.The number of loops is dependent on the width and, preferably, each loopis 6 centimeters long. The loops are positioned in such a way that in alay-flat position, the loops of the top and bottom external layers willbe adjacent to and alternating with each other in an interlaced manner.See FIGS. 4-6.

In the fourth step, a top mounted load/discharge valve is attached tothe inner liner through an opening on the top external layer centrallyplaced widthwise and near one end seam lengthwise, preferably about 30to 36 inches from the end seam. The valve is preferably secured using aclamp. The inner liner, with its 2-4 layers already formed and weldedtogether at the ends, is inserted through the open end of the bag nearerthe valve and positioned between the top and bottom layers. Any “coupon”of the inner liner at the closed end of the bag is tucked so that itlays flat against the outer layers. Any “coupon” of the inner liner atthe open end of the bag is tucked and then the additional layer offabric is moved from the position of dashed line A in FIG. 7(b), so asto cover the end and the coupon of the inner liner as shown in FIG. 7(d)and be positioned over the top of the inner liner.

In the final step, the nylon rope is threaded through the alternatinginterlaced loops of the open ends of the bag completely across theseams. The rope closes the seams and secures the flexitank into thecover. Alternatively, grommets may be used in place of the alternatingloops to lace it together. When the bag is filled with liquid as shownin FIG. 7(e), the inner liner expands pushing against the end flap andagainst the end closures with the loops. It is to be noted that theloops in the end closure are not watertight and are not intended to bewatertight. The end flap provides some protection against leakage butprimarily provides additional strength to the end closure. The end flapcontains the inner liner inside the external layers of the cover,stopping it from coming into direct contact with the end closure. Asshown in FIG. 8, the loops do not remain in alignment and the rope doesnot remain straight when the flexitank is filled, but they do provideend-closures of significant strength.

The closure provides an extremely high strength which is particularlyuseful for the end closures of flexitanks. However, the closure islimited in its use to the preferred embodiments described herein. It canalso be used for the sides of a rectangular shaped flexitank, oranywhere a higher strength replacement for a sewn seam is desired. Theend closures here are based on those disclosed in PCT InternationalApplication No. PCT/US2018/058530 filed on Oct. 31, 2018, and U.S.Provisional Patent Application 62/579,612 filed on Oct. 31, 2017, thosedisclosures being incorporated by reference herein.

An alternative preferred embodiment of the end closure is shown in FIG.9. In addition to the inner and outer layers, and end flap C, of thepreferred embodiment shown in FIGS. 7(a)-7(e), an additional end cap Cis secured to the end of the inner layer. End cap C is formed from alayer of PVC fabric in a rectangular shape that is, for a flexitankhaving the preferred dimensions noted above, about 116″ wide×60″ long.It is folded in half making it 116″ wide×30″ overall. The folded overmaterial is then welded on each of the 30″ long sides making the productshaped like a canoe if filled with water. This additional layer at acritical point adds strength overall to the end closure system. The endcap C helps to form the shape of the flexitank and further strengthen itagainst the large liquid dynamic forces resulting from the suddenstarts, stops and jolts of a railroad car.

In addition to the above features, where a container has a door recesschannel directly inside its doors, a bulkhead system may be insertedinto that recess channel. The bulkhead system may be the bulkhead systemshown in the end view of FIG. 10 and the side view of FIG. 11. There aremultiple square bars 5 of 3/16^(th) steel tube stock that fit into thedoor post slots. Although five bars are shown in FIGS. 10 and 11, theremay be four or six such bars. A bottom telescopic bar 2 is preferablyformed of a steel tube and includes an inner telescopic steel tube 3.Two vertically oriented short-straps 4 are preferably steel flat barsthat secure steel bars 5 and telescopic bar 2 together, such as withhexagonal bolts at the overlap of the bars and each short-strap. Thesteel bars 5 and telescopic bar 2 protrude horizontally to secure thebulkhead into the recess channel and provide 2 inches of clearance fromthe bulkhead to the door. A corrugated polypropylene fluted panel board1 is secured to each bulkhead bar 5 and telescopic bar 2 by passing zipties through the corrugated board 1 and around the respective bar. Theboard is preferably thick, such as 10-12 mm. The container walls arealso lined with single wall corrugated paper, preferably without anyadditional side or wall reinforcement.

1. A flexible tank for transporting bulk liquids or semi-liquidmaterials in a shipping container on a railroad car, comprising: aninterior tank made of a flexible water-proof polymeric material, saidinterior tank being generally rectangular in shape with a width of atleast one end of the interior tank being less than the length of theinterior tank, the interior tank enclosing within it the bulk liquid orsemi-liquid materials being transported; a first exterior layer made ofa flexible polymeric material in a generally rectangular shape, a firstend of the first exterior layer having a series of hollow loops andspaces between the hollow loops in a widthwise direction along the firstend, the hollow loops and spaces alternating in sequence; a secondexterior layer made of a flexible polymeric material in a shape and sizesubstantially similar to the first exterior layer, a first end of thesecond exterior layer having a series of hollow loops and spaces betweenthe hollow loops, the hollow loops and spaces alternating in sequence inthe widthwise direction of the first exterior layer, the first end ofthe second exterior layer being matched up with the first end of thefirst exterior layer such that the hollow loops of the second exteriorlayer occur at the positions of the spaces of the first exterior layerand the spaces of the second exterior layer occur at the positions ofthe hollow loops of the first exterior layer; a plurality of capacitybands located around the outer periphery of the second exterior layer,each one of said plurality of capacity bands constraining the expansionof the flexible tank at its location during movement of the railroadcar; and a rope, the rope passing through the alternating hollow loopsof the first and second exterior layers and connecting the first andsecond exterior layers to each other, the interior tank beingconstrained within the first and second exterior layers connected by therope.
 2. The flexible tank of claim 1, wherein the flexible tank is lessthan the length of the shipping container and is not supported by theend walls of the shipping container.
 3. The flexible tank of claim 1,wherein the flexible tank has a capacity of more than 8,000 liters.
 4. Amethod of transporting bulk liquids or semi-liquid materials in aflexible tank in a shipping container on a railroad car, comprising:folding over the ends of rectangular shaped first and second layers offlexible polymeric material to form a continuous loop over the entiretyof the width of said ends of said first and second layers; connectingthe longitudinal sides of the first and second layers to form an openended tube; attaching a first end of a first end flap to the inside ofone of the first and second layers near a first end of the open endedtube and a first end of a second end flap to the inside of one of thefirst and second layers near a second end of the open ended tube, thelength of the first end flap being greater than the distance from itspoint of attachment to the first end of the open ended tube and thelength of the second end flap being greater than the distance from itspoint of attachment to the second end of the open ended tube; cuttingportions from each one of the continuous loops of said ends of saidfirst and second layers so as to become a sequence of alternating hollowloops and spaces, the hollow loops and spaces of the first layerinterlacing with the hollow loops and spaces of the second layer;inserting an inner liner into the interior space of the open ended tubeformed by connecting the longitudinal sides of the first and secondlayers, the inner liner made of a flexible water-proof polymericmaterial so as to enclose within it the bulk liquid or semi-liquidmaterials being transported; moving the respective second ends of thefirst and second end flaps to cover the ends of the inner liner; closingthe first and second ends of the flexible tank with the inner liner andend flaps constrained therein by threading a rope between the interlacedhollow loops of the first and second layers; and placing a plurality ofcapacity bands at locations around the outer periphery of the flexibletank, each one of said plurality of capacity bands constraining theexpansion of the flexible tank at its respective location duringmovement of the railroad car, the flexitank reliably not leaking duringaccelerations and decelerations of the railroad card.
 5. The flexibletank of claim 4, wherein the flexible tank is less than the length ofthe shipping container and is not supported by the end walls of theshipping container.
 6. The flexible tank of claim 4, wherein theflexible tank has a capacity of more than 8,000 liters.